While the participants were in the scanner, the researchers focused their attention on the visual cortex, the portion of the brain that processes what you see and is particularly sensitive to aging. The superagers' memory was indistinguishable from that of 25-year-olds in the fMRI research, and their visual brain activity patterns remained youthful.

Our brains usually shrink as we become older, resulting in weaker connections between various areas of the brain, which leads to memory and other cognitive skills deteriorating. However, a small subset of older people known as "superagers" have been found to learn and retain new knowledge at the same rate as a 25-year-old.

The brain activity that underlies superagers' enhanced memory has now been pinpointed by researchers at Massachusetts General Hospital (MGH).

"This is the first time we have images of the function of superagers' brains as they actively learn and remember new information," says Alexandra Touroutoglou, PhD, director of Imaging Operations at MGH's Frontotemporal Disorders Unit and senior author of the paper published in Cerebral Cortex.

In 2016, Touroutoglou and her colleagues discovered a group of individuals over 65 who performed exceptionally well on memory tests. The superagers are part of an ongoing longitudinal aging study at MGH directed by Bradford Dickerson, MD, director of MGH's Frontotemporal Disorders Unit, and Lisa Feldman Barrett, PhD, a research scientist in MGH's Psychiatry department.

"Using MRI, we found that the structure of superagers' brains and the connectivity of their neural networks more closely resemble the brains of young adults; superagers had avoided the brain atrophy typically seen in older adults," says Touroutoglou.

In the recently published study, the researchers gave 40 individuals a difficult memory test while imaging their brains with functional magnetic resonance imaging (fMRI), which, unlike traditional MRI, reveals the activity of distinct brain regions during tasks. While their brains were scanned, 41 young people (mean age: 25) performed the identical memory test.

The participants were shown 80 images of faces or settings, each of which was matched with an adjective, such as a cityscape with the term "industrial" or a masculine face with the term "average." Their first duty was to see if the word matched the image, which is known as encoding.

After 10 minutes, the participants were given with the 80 image-word pairings they had just learned, 40 new words and images, and 40 rearranged pairs of words and images they had seen earlier. Their second goal was to remember whether they had seen each word-picture pair before or if they were looking at a fresh or rearranged pair.

The researchers focused their attention on the visual cortex, which is the region of the brain that processes what you see and is particularly vulnerable to aging, while the individuals were in the scanner.

"In the visual cortex, there are populations of neurons that are selectively involved in processing different categories of images, such as faces, houses or scenes," says lead author Yuta Katsumi, PhD, a postdoctoral fellow in Psychiatry at MGH. "This selective function of each group of neurons makes them more efficient at processing what you see and creating a distinct memory of those images, which can then easily be retrieved."

This selectivity, known as neural differentiation, decreases with age, and the group of neurons that used to respond only to faces now responds to other pictures. The brain is currently having trouble generating separate neural activity patterns for different sorts of pictures, implying that it is producing less distinct mental representations of what the individual is viewing.'

In the fMRI analysis, however, the superagers' memory was indistinguishable from that of 25-year-olds, and their visual cortex activity patterns remained young.

"The superagers had maintained the same high level of neural differentiation, or selectivity, as a young adult," says Katsumi. "Their brains enabled them to create distinct representations of the different categories of visual information so that they could accurately remember the image-word pairs."

"An important question that researchers still must answer is whether 'superagers' brains were always more efficient than their peers, or whether, over time, they developed mechanisms to compensate for the decline of the aging brain," says Touroutoglou.

The researchers are currently undertaking a clinical study to see if noninvasive electromagnetic stimulation, which provides an electrical current to specific regions of the brain, may help older individuals enhance their memory. The researchers are also aiming to look at other brain areas to discover more about how superagers learn and recall, as well as lifestyle and other variables that may play a role in superagers' incredible memory.

The study was published on June 30th, 2021, in Cerebral Cortex.

Abstract. We assessed the fidelity of neural representations as participants encoded and later retrieved a series of word stimuli paired with a face or a scene image. Superagers, like young adults, exhibited more distinct neural representations in the fusiform gyrus and parahippocampal gyrus while viewing visual stimuli belonging to different categories (greater neural differentiation) and more similar category representations between encoding and retrieval (greater neural reinstatement), compared with typical older adults. Greater neural differentiation and reinstatement were associated with superior memory performance in all older adults. Given that the fidelity of cortical sensory processing depends on neural plasticity and is trainable, these mechanisms may be potential biomarkers for future interventions to promote successful aging.

Yuta Katsumi, Joseph M Andreano, Lisa Feldman Barrett, Bradford C Dickerson, Alexandra Touroutoglou, Greater Neural Differentiation in the Ventral Visual Cortex Is Associated with Youthful Memory in Superaging, Cerebral Cortex, 2021;, bhab157, https://doi.org/10.1093/cercor/bhab157